1. Technical Field
The present invention relates to an electronic device including a photosensitive adhesive which is interposed between two substrates and bonds the two substrates, and a manufacturing method of the electronic device.
2. Related Art
An electronic device includes a piezoelectric element or the like which is deformed by a voltage that is applied, and is used for various devices, various sensors, or the like. For example, in a liquid ejecting apparatus, liquid of various types is ejected from a liquid ejecting head which uses an electronic device. The liquid ejecting apparatus includes an image recording apparatus such as, an ink jet type printer or an ink jet type plotter, but recently, the liquid ejecting apparatus has been also used for various manufacturing apparatuses by utilizing features in which a very small amount of liquid can be correctly landed on a predetermined position. For example, the electronic device is used for, for example, a display manufacturing apparatus which manufactures a color filter such a liquid crystal display, an electrode forming apparatus which forms electrodes of an organic electro luminescence (EL) display, a field emission display (FED), or the like, and a chip manufacturing apparatus which manufactures a biochip (biochemical element). Then, a recording head for an image recording apparatus ejects ink of liquid type, and a color material ejecting head for a display manufacturing apparatus ejects solutions of each color material of red (R), green (G), and blue (B). In addition, an electrode material ejecting head for an electrode forming apparatus ejects an electronic material of liquid type, and a bio-organic substance ejecting head for a chip manufacturing apparatus ejects a solution of a bio-organic substance.
The liquid ejecting head includes a pressure chamber forming substrate in which a pressure chamber communicating with a nozzle is formed, a piezoelectric element (a type of a drive element) which causes a pressure change to occur in liquid within a pressure chamber, and an electronic device in which a sealing plate or the like that is disposed so as to be separated from the piezoelectric element with an interval is stacked. In recent years, a technology has been developed in which a drive circuit (also referred to as a driver circuit) for driving an piezoelectric element is provided on the sealing plate. The sealing plate is bonded to a pressure chamber forming substrate in which a piezoelectric element is stacked, in a state in which a bump electrode is interposed therebetween (for example, JP-A-2014-51008). As a result, the drive circuit and the piezoelectric element are electrically coupled to each other through the bump electrode.
In addition, a technology is developed in which an adhesive (photosensitive adhesive) configured by a resin or the like with photosensitivity is used for the above adhesive. If such an adhesive is used, one substrate is first coated with an adhesive of liquid type by using a spin coater or the like, and the adhesive is cured to a certain degree by heating. Then, by performing exposure and development, the adhesive is patterned in a predetermined position. Thereafter, by attaching the other substrate so as to face the one substrate, curing the adhesive by heating again, and thereby both the substrates are bonded together. As a result, the adhesive can be correctly patterned in a predetermined position.
If the above-described photosensitive adhesive is used, it is possible to prevent a shape after development from being collapsed, and thus a degree of cure is performed to a certain degree of cure. For this reason, when both the substrates are bonded together, adhesion (that is, bonding strength) to the other substrate by an adhesive decreases. Particularly, if there is roughness on a surface (adhered surface) of the substrate, adhesiveness of the adhesive decreases, the adhesion remarkably decreases.